The present invention relates to wireless communications, more particularly to power management of sensor nodes of a wireless sensor network.
The United States Navy uses sensors (detectors) to maintain situational awareness in association with shipboard electromechanical systems such as machinery automation and control systems. Sensors useful for such purposes include position sensors, temperature sensors, chemical compound sensors, infrared (IR) sensors, image spectrum analyzers, etc. Networking of sensors has traditionally involved wiring—i.e., wired powering of sensors, and wired communication between sensors. Wireless networking of sensors is being considered and developed by the Navy because of beneficial prospects of distribution, decentralization, survivability, and reconfigurability as pertain to machinery automation and control for ship operations.
Power can be supplied to a sensor via conventional approaches such as wiring (e.g., shipboard wiring) from a power source (direct current or alternating current), or close association of a direct current power supply with (e.g., embedment of one or more batteries in) the sensor. Cumbersome, proliferative wiring is often undesirable or impractical. Direct current power sources such as batteries run out of power and require replacement or continual recharging.
It is known generally that energy can be harvested from ambient sources such as light (electromagnetism), sound, vibration, heat, etc. A solar cell, for instance, is a common type of energy harvester. Recent literature has disclosed management of power consumption in wireless systems, such as through energy (power) harvesting, and/or power reduction (e.g., “sleep mode”) under prescribed circumstances. Some energy harvesting technologies require communication devices to periodically sleep in duty cycles so that energy can be harvested and stored. Due to the variability of environmental energy sources for harvesting, energy harvesting technology may provide a very low duty cycle with an event-triggered interrupt function. See, e.g., the following United States patents: Townsend et al. U.S. Pat. No. 7,764,958 B2, Arms et al. U.S. Pat. No. 7,719,416 B2, Hamel et al. U.S. Pat. No. 7,429,805 B2, Cohen U.S. Pat. No. 7,400,253 B2, Arms et al. U.S. Pat. No. 7,256,505 B2, Hamel et al. U.S. Pat. No. 7,081,693 B2, incorporated herein by reference. See also, Ortiz et al., “Energy Harvester Power Management for Wireless Sensor Networks,” ASNE Proceedings, Automation and Controls Symposium, 10-11 Dec. 2007, Biloxi, Miss., incorporated herein by reference.
While energy harvesting appears to represent a piece of the puzzle, there is plenty of room for improvement for implementing energy harvesting in the context of a wireless sensor network so as to supply power to each sensor node in an economical, sustainable, and feasible manner.